1. Field of the Invention
This invention relates to rotary fluid control valves of the butterfly type wherein a disc is mounted for rotation between the open position, in which the disc lies substantially parallel to the axis of the fluid flow channel through the valve, and the closed position in which the disc lies perpendicular to this axis. The disc, in its closed position, cooperates with an annular flexible seat circumscribing the fluid flow channel to shut off fluid flow through the channel. The annular flexible seat is held in position by being clamped in a recess formed between complementary surfaces of a portion of the valve body and a valve seat insert. The insert may be bolted to the valve body, or more commonly, the insert is fixed in position when the valve is bolted between the pipe flanges formed on the pipes that convey fluid to and from the valve.
2. Description of the Prior Art
With a butterfly valve of the type just described, it is desirable to provide features that will optimize the sealing effectiveness of the valve, yet minimize certain disadvantages apparent in prior art butterfly valves. For example, it is advantageous for a butterfly valve to provide a tight seal regardless of the direction of fluid flow, and continue to do so despite continuous reversal of pressure differentials across the valve. Further, pressure up to and including the full valve pressure rating should be appliable from either direction without leakage across the valve.
Butterfly valves are frequently subjected to a wide range of temperatures, both from the ambient environment in which they operate and from the flowing media being controlled. Further, the temperature will frequently cycle over a relatively wide range and it is advantageous for a butterfly valve to withstand these temperature variations without adverse effects on its sealing capabilities.
When a butterfly valve is installed for operation, it is generally bolted between pipe flanges on the fluid supply pipes. Gaskets are provided between each flange and the flange-facing side of the valve body. When the bolts are tightened, the above mentioned valve insert is compressed flush with the face of the valve body, thereby compressing the portion of the annular seat that is gripped in the recess formed between insert and body. This compression of a portion of the seat can cause distortions in the seat configuration that adversely affect the sealing contact between seat and disc edge if the disc is not fully closed during installation and can increase the force necessary to overcome the torque of the valve during opening and closing of the valve. Accordingly, it is advantageous for a butterfly valve to have a seat that is insensitive to disc position upon installation and to have torque and sealing characteristics that are not affected by flange and gasket compression.
The above mentioned advantages as well as others and the manner of their attainment, will become apparent to those skilled in the art from a consideration of this specification when taken in conjunction with the appended drawing.